1. Field of the Invention
The invention relates to drill pipe for subterranean wells, and the like, having upset areas adjacent the area of securement thereof to a tool joint.
2. Brief Description of the Prior Art
When drill pipe is used to drill subterranean wells, the pipe is exposed to bending stresses. Such bending stresses are primarily due to hole curvatures extending through the entire length of the drilled hole. Such stresses may cause fatigue of the drill pipe due to fluctuating reversed bending stress which is imposed during rotation of the drill pipe. If the drill pipe fails by such resulting fatigue, the location of the fatigue point is oftentimes approximate the area of securement at the lowermost end thereof, i.e., from about 1 to about 5 feet from the point of securement of the end of the pipe to the tool joint. The stress in this portion of the drill pipe is usually considerably higher than the stress which is imposed on the remaining portions of the drill pipe conduit.
Applicant is aware of the following prior art which is addressed to similar problems of stress on subterranean well conduits, but which does not anticipate or render obvious the present invention: (1) U.S. Pat. No. 4,416,476, issued Nov. 22, 1983, and entitled "Intermediate Weight Drill Stem Member"; and (2) U.S. Pat. No. 1,325,073, issued Dec. 16, 1919, and entitled "Method Of Forming Coupling Ends On Drill Tube Sections".
The present invention addresses some of the deficiencies as described in the prior art.